Before you begin using a medication, be sure to inform your doctor of any medical conditions or Allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use Pegasys (Peginterferon-alfa-2a).

Allergic reactions: In rare cases, Pegasys (Peginterferon-alfa-2a) may cause severe allergic reactions. If you notice hives, swelling of the face or throat, or difficulty breathing, stop using Pegasys (Peginterferon-alfa-2a) and get medical help immediately.

Autoimmune conditions: Pegasys (Peginterferon-alfa-2a) may cause or worsen autoimmune conditions including myositis, hepatitis, immune thrombocytopenic purpura (ITP), Rheumatoid Arthritis, interstitial nephritis, thyroiditis, and systemic Lupus erythematosus. If psoriasis appears, the medication may need to be discontinued.

Blood glucose (sugar): Pegasys (Peginterferon-alfa-2a) can cause low or high blood sugar. People with Diabetes should discuss with their doctor how Pegasys (Peginterferon-alfa-2a) may affect their medical condition, how their medical condition may affect the dosing and effectiveness of Pegasys (Peginterferon-alfa-2a), and whether any special monitoring is needed. If you experience high blood sugar (increased thirst, hunger, weakness, drowsiness, blurred vision, weight loss) or low blood sugar (headache, hunger, weakness, irritability, trouble concentrating) while taking Pegasys (Peginterferon-alfa-2a), contact your doctor.

Blood problems: Pegasys (Peginterferon-alfa-2a) may suppress bone marrow function and cause blood problems such as low platelet counts, low white blood cell counts, and anemia. Your doctor will monitor you for these problems with blood tests. If you experience persistent fever and chills, tiredness, shortness of breath, or easy bruising or bleeding, contact your doctor.

Colon disorders: Pegasys (Peginterferon-alfa-2a) may cause certain types of colitis. Report any stomach or abdominal pain, bloody diarrhea, or fever to your doctor immediately.

Depression and other psychiatric conditions: Pegasys (Peginterferon-alfa-2a) can cause depression and other psychiatric conditions. People with psychiatric conditions should be closely monitored by their doctor while using Pegasys (Peginterferon-alfa-2a), as it may worsen these conditions.

If you experience symptoms of depression such as poor concentration, changes in weight, changes in sleep, decreased interest in activities, or notice them in a family member who is taking Pegasys (Peginterferon-alfa-2a), contact your doctor as soon as possible.

Dizziness/reduced alertness: Peginterferon alfa-2a may affect the mental or physical abilities needed to drive or operate machinery. Avoid driving, operating machinery, or performing other hazardous tasks until you have determined how Pegasys (Peginterferon-alfa-2a) affects you.

Eye disorders: Certain eye disorders have been observed in people using Pegasys (Peginterferon-alfa-2a). If you experience any changes in vision while taking Pegasys (Peginterferon-alfa-2a), contact your doctor.

Flu-like symptoms: Pegasys (Peginterferon-alfa-2a) may cause a flu-like reaction with aching muscles, fever, chills, and headache. Your doctor may prescribe Acetaminophen before each dose of Pegasys (Peginterferon-alfa-2a) and as needed to help reduce these symptoms.

Fluids: Pegasys (Peginterferon-alfa-2a) may cause dehydration. People taking Pegasys (Peginterferon-alfa-2a) should drink adequate fluids, especially on hot days or when exercising.

Heart disease: Pegasys (Peginterferon-alfa-2a), as well as others like it, can cause heart problems such as high blood pressure, chest pain, heart attack, abnormal heart rhythms, and heart failure. If you have had a heart attack, heart failure, or changes in heart rhythm (Arrhythmias), discuss with your doctor how Pegasys (Peginterferon-alfa-2a) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Pegasys (Peginterferon-alfa-2a), and whether any special monitoring is needed. People with severe, unstable, or uncontrolled heart disease should not use Pegasys (Peginterferon-alfa-2a).

Kidney Disease: People with kidney disease should discuss with their doctor how Pegasys (Peginterferon-alfa-2a) may affect their medical condition and whether any special monitoring is needed. People with reduced kidney function may require a lower dose.

Liver function: People who are taking Pegasys (Peginterferon-alfa-2a) will need frequent checkups to test their liver function. People with reduced liver function may require a lower dose of the medication or may need to stop taking it.

Lung disorders: Certain lung disorders may occur in people using Pegasys (Peginterferon-alfa-2a), causing breathing difficulty. These conditions can be fatal. If you experience fever, cough, or shortness of breath, contact your doctor as soon as possible.

Pancreatitis: Pegasys (Peginterferon-alfa-2a) may cause pancreatitis, which may be fatal. If you develop symptoms of pancreatitis (e.g., severe abdominal pain with or without vomiting), get immediate medical attention.

Stroke: Pegasys (Peginterferon-alfa-2a) has been associated with strokes. If you experience symptoms of a stroke (e.g., sudden and severe headache, sudden weakness or numbness in the arms or legs, sudden vision changes, sudden dizziness) while taking Pegasys (Peginterferon-alfa-2a), get immediate medical attention.

Thyroid disorders: Pegasys (Peginterferon-alfa-2a) can cause or worsen Hypothyroidism (low thyroid) or Hyperthyroidism (high thyroid). People with thyroid conditions should discuss with their doctor how Pegasys (Peginterferon-alfa-2a) may affect their medical condition, how their medical condition may affect the dosing and effectiveness of Pegasys (Peginterferon-alfa-2a), and whether any special monitoring is needed.

Transplants: The safety and effectiveness of using Pegasys (Peginterferon-alfa-2a) have not been established for people who have had a liver or other organ transplant.

Pregnancy: Pegasys (Peginterferon-alfa-2a) should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking Pegasys (Peginterferon-alfa-2a), contact your doctor immediately. Women who may become pregnant should use an effective method of birth control while using peginterferon alfa-2a.

Breast-feeding: It is not known if peginterferon alfa-2a passes into breast milk. If you are a breast-feeding mother and are taking Pegasys (Peginterferon-alfa-2a), it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children and adolescents: The safety and effectiveness of using Pegasys (Peginterferon-alfa-2a) have not been established for children under the age of 18. Pegasys (Peginterferon-alfa-2a) is not recommended for use by newborns or infants because peginterferon alfa-2a contains benzyl alcohol and may be harmful.